The Case of the “Low-Yield” Trident Warhead

Among the nuclear weapons programs included in the Trump administration’s Nuclear Posture Review, only one could start this year and be fully implemented in 2019. The military could field a “low-yield” nuclear warhead for the Trident missiles carried by US submarines.

What is this new warhead capability, and where does the proposal stand?

The NPR describes it as a “near-term” effort to “modify a small number of existing SLBM warheads to provide a low-yield option.”

The plan, according to Hill staff I have spoken to and former officials, is to implement this change as a part of the life extension program for the W76 warhead, which is scheduled to wrap up in—you guessed it—Fiscal Year 2019.

The explosive yield of the W76 is 100 kilotons of TNT. The explosive power of this “low-yield” version, according to information given classified briefing and then told to me, is apparently around 5 kilotons of TNT, or one-third the size of the Hiroshima bomb that killed 100,000 people. So, while the new weapon would have a “lower” yield, it would still be substantial.

To achieve this lower yield, according to informed sources, the National Nuclear Security Administration (NNSA) would remove the secondary, or second stage, from the W76 warhead, and replace it with an inert version that has the same size and weight and weight distribution. Then, presumably, they would adjust the amount of deuterium/tritium gas in the primary, or first stage, of the nuclear warhead to achieve the desired yield. The gas is used to increase the yield of the primary relative to that of just the plutonium. (See the diagram. For a primer on nuclear weapons, see here.)

The NNSA already does this because such changes are required for all missile test flights; they cannot use live warheads, so they use a dummy warhead with inert replacements for the primary and secondary that are of equal size, weight, and weight distribution. In this case, they would only replace the secondary and, if plans proceed, the NNSA would perform the work as a part of the W76 life extension program.

According to the then-acting head of the NNSA, Steven Enhart, at a recent conference I attended, the new warhead will be dubbed the W76-2. He also confirmed the weapon would have a “primary-only” yield.

What we don’t know is how much all this will cost. Relative to the Pentagon’s budget, it will be small. However, when the Fiscal Year 2019 budget was released on February 5, not a trace of money for the program was identified, either in the Department of Defense budget (responsible for the missile) or Department of Energy budget (responsible for the warhead). A Navy official even briefed reporters that there was no money in the budget for it.

But there is in fact money for the low-yield warhead in the DOD budget. Rob Soofer, who chaperoned the NPR for the Pentagon, stated in public on several occasions that the FY19 budget had $22.6 million for it and around $50 million in total is planned through FY2023.

That still did not explain where in the DOD budget the money was. I was recently provided three documents that do explain it, albeit informally. This extract from the FY19 DOD budget request, shows funding requested for the Trident missile life extension program, a 20-year long, $24 billion project to rebuild and improve the entire missile. Buried on page 23 of that document is a line item for “Warhead Components” funded at $87.33 million for FY19. In the document as provided to me, you can see the yellow highlight with a comment on the PDF.

A second document I was provided—written answers that the Pentagon provided to questions the House and Senate Defense appropriations subcommittees submitted—provides a more readable listing of $22.6 million figure. It also states the total funding through FY2023 is $48.5 million.

To get the year-by-year funding that makes up the $48.5 million total, we have to turn to the third, rather modest document I was given, this an Excel file that I converted to this image:

It shows the most funding is in FY19, followed by $19 million in FY20, and $3.2 million or less for the next three years.

However, these documents still leave two important questions unanswered.

First, what is the DOD money for?

This program is to modify a warhead, and that work is entirely the provenance of the NNSA, not DOD. As the Pentagon’s answers to questions from the Hill state: “The NNSA is studying the concept and will produce the actual low-yield nuclear warheads[.]”

However, the DOD will also have work to do. In the first document I was provided, it includes (on page 3) this opaque language under the heading “Changes from FY18 to FY19”:

-Increase in Warhead Components to support the ‘-3 Option’ program initiation efforts including but not limited to, evaluating and updating requirements documentation, SPALT [Strategic Programs Alteration] development, updating facility handling/processing documentation, development of implementation concept of operations, initiation of the qualification efforts, and safety study and DoE production engineering.

Although there is no explicit reference to a low-yield warhead and therefore it could refer to something else, the language evokes the deployment of a new capability. No where else in the document is the ‘-3 Option’ mentioned.

Second, the greater mystery is what the NNSA is doing. When the FY19 administration budget request was released on February 5, the full NNSA budget was not even available, merely topline numbers from the full federal budget released by the Office of Management and Budget. Eleven days later, the NNSA volume was released, and still included no money for the low-yield warhead.

Because it does not, the DOE must now work with Congress to add it into the budget, via a supplementary budget request or some other agreement. And staff on the House Armed Services Committee have publicly stated that funding for the program must be authorized and appropriated for it to proceed; the DOD and DOE cannot simply run off and do it.

As to how much it would cost the NNSA, I was informed that one representative from Los Alamos national laboratory (the institute responsible for design and development of the nuclear components of the W76) told officials that the change could be made for zero dollars. That seems unlikely to be true, given that some procedures will have to be developed, but it does imply that the cost will not be large.

But just how much it will cost and how it will be done, the NNSA does not know or it is not yet willing to say. The week the Strategic Forces Subcommittee of the Senate Armed Services Committee held a hearing with Lisa Gordon-Hagerty, the newly-appointed NNSA head. Sen. Elizabeth Warren pressed the administrator with a series of questions, including: How many warheads will be modified to be low-yield? How long will it take to modify the warheads? Can the NNSA complete it as a part of the life extension program for the W76 warhead?

Administrator Gordon-Hagerty was prepared, in a follow-up classified session, to tell Sen. Warren how many warheads would be modified, but had no answers for the rest of her questions, saying the NNSA was still studying the issue and working with the Nuclear Weapons Council (a joint DOD-DOE body responsible for overseeing the stockpile).

Sen. Warren’s questions were not idle. She was one of sixteen senators who sent a letter to President Trump expressing alarm about the low-yield capabilities proposed in the NPR, declaring that they “are unnecessary to maintain deterrence and are destabilizing.” There is certain to be a fight in Congress over this program.

In sum, what do we know?

The DOD has requested some modest funding – $22.6 million in FY19 and $48.5 million through FY23 – for the low-yield warhead, but it isn’t clear what that funding is for.

The new warhead will be called the W76-2.

The DOE must do work to make it happen but has not finished its plan to do so.

The amount of money DOE will require is likely to be relatively small and the technical work required is relatively straightforward.

Congress must authorize and appropriate funding for the project to move forward, but the fact that the program was not in the DOE budget request somewhat complicates that.

There will be a fight in Congress over this new capability.

For its part, UCS will be among those opposing the low-yield warhead. We have already published a couple of initialtakes on the NPR, and have significant problems with it. You can expect a more detailed critique of the low-yield option soon.

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